Throwing a party or celebrating an event before it is appropriate. Most often done in an effort to fit the schedule of someone other than the party honoree.
Kelly: Why are we having cake today? Isn't Cara's birthday next Friday?

Mark: Yeah, but her boss is on vacation next week, so we're having a premature celebration.
by Fireball D May 7, 2009
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golf term: The use of any celebratory action (ie. fist pump, raised arm, verbal comment etc.) assuming a putt will go into the hole before the ball actually enters the hole thus causing the ball to miss. Very mysterious phenomenon which plagues golfers.
I had that putt made until Steve went into a premature celebration and caused it to lip out
by goodbuddygolfer September 16, 2010
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